Oil shale is a naturally occurring material which contains a hydrocarbonaceous component referred to as kerogen. Upon heating, the kerogen decomposes to release a hydrocarbon vapor which may be used as a feedstock in petroleum processing. This synthetic crude oil called "shale oil" contains relatively high levels of iron, arsenic, and nitrogen as compared to conventional petroleum. In addition, due to the fissile nature of the raw oil shale and to the friability of the inorganic residue remaining after pyrolysis, the shale oil is also contaminated with a significant amount of fine solids which may constitute as much as 10% by weight of the pyrolysis oil. This contamination usually must be reduced prior to downstream processing to prevent poisoning of the various catalysts and clogging of the equipment.
Another naturally occurring raw material for production of pyrolysis oil is tar sand that occurs in a variety of forms including fine-grain diatomite. In analogy to the kerogen in oil shale, bitumen in tar sands may be pyrolyzed to yield a pyrolysis oil similar to shale oil. Particulate contamination in tar sands derived oil is similar to that in shale oil.
The present invention is directed to a process for recovering pyrolysis oil from oil shale or tar sand of significantly reduced contamination and having a lower average molecular weight than otherwise may be recovered by the pyrolysis of these raw materials.